TYSONS CORNER, Va. – The Express Lanes being built on the Virginia side of the Capital Beltway aren’t officially open yet, but that doesn’t mean cars aren’t driving on them.

A number of test vehicles started cruising the brand new lanes this week. The test is all about the electronics of the road.

Drivers will need either a traditional E-ZPass or E-ZPass Flex transponder to ride in the lanes. There are no toll booths on the road.

The test vehicles are out on the lanes to make sure the overhead electronic gantry system is working properly. That gantry will tack a toll directly onto the E- ZPass, similar to the way the InterCounty Connector operates in Maryland.

“The full functionality of the 495 Express Lanes’ tolling and traffic management system is essential to the success of the 495 Express Lanes. This testing phase is critical to ensure that our systems are ready to deliver faster and more predictable travel to drivers,” says 495 Express Lanes General Manager Tim Steinhilber in a statement.

The action in the Express Lanes is clearly visible to those traveling in the regular Beltway Lanes, and because of that, there is some caution from Steinhiber.

“It is important that drivers stay alert and do not follow these vehicles into the Express Lanes,” he says.

The testing is expected to last until the end of August.

By the end of 2012, two new Express Lanes will be open in each direction between Springfield and just north of the Dulles Toll Road.

Carpools with three or more people can use the lanes, which promise a minimum speed of around 55 miles per hour, for free.

Cars with fewer than three people can use the lanes, but those vehicles will have to pay a variable toll that will rise and fall depending on how much traffic is in the lanes.

The new E-ZPass Flex transponder has a switch that allows drivers to toggle between High Occupancy Vehicle (HOV) mode of three or more people to non-HOV mode of fewer than three people.

Virginia State police are anticipating some riders might leave the switch in HOV mode permanently and try to ride in the lanes for free. They are dedicating a force of state troopers to constantly monitor the lanes and spot HOV cheaters. Technology will alert police when a car has the flex transponder switched to carpool mode.

The current cost estimate of the Express Lanes project is $1.9 billion. The project is being funded with both public and private money.